As is well known, MR imaging uses an RF receive coil to receive the signals emitted by the subject under test in response to excitation of a selected volume of the subject. Thus the Gradient coils generate controlled variations in the main magnetic field (B0) magnetic field to produce selected spatial excitation volume and the signal emitted by that selected volume is picked up by the receive coil arrangement and transmitted to a signal processing system.
The receive coil arrangement can comprises a single coil loop or element or it can include a series of loops arranged in a pattern around the part of the subject to be imaged.
Hereinafter, the term “loop” is used for one component or element of a complex receive coil arrangement and this term is not intended to limit the shape or structure of the individual elements defined by this term. Typically each loop is a single loop with a conductive wire or other conductive material so that current flows around the loop in response to the signal. Different materials can be used for the conductive material and certainly the terms used herein are not limited to specific materials which can be used.
Normally, each individual loop or loops of the MRI receive coil arrangement are connected to a single receiver of the signal processing system via preamplifier and other components with a cable.
Such receive coil arrangements can therefore use the so called “built in body coil” carried on the magnet as receive coil which is connected by cable to the signal processing system. In this case the so called “built in body coil” is also used as transmit coil
Such receive coil arrangements can therefore comprise a single loop which is connected by a single wire to a single channel of the signal processing system. In this case the system can use the so called “built in body coil” carried on the magnet as transmit coil. This signal loop receive coil then supplies the received signal collected around the subject, typically a lying patient, and communicates it to the single channel for processing using conventional systems well known to persons in this art.
Such receive coil arrangements can therefore comprise a multiple loop arrangement including a so-called “phased array” of loops each of which is connected by a respective wire to a separate one of a plurality of channels of the signal processing system.
In this case the system typically uses a portable coil assembly arranged to wrap around the body part of the patient but each loop must have its own set of processing components and its own wire connecting the signal to the separate channel for processing.
However in recent developments not yet widely adopted, the “built in body coil” carried on the magnet as the receive coil arrangement is separated into individual loop components for supplying a separate signal to the separate channels.
It is well known that there are parallel imaging techniques to reduce the time necessary to obtain a complete scan of the part of the patient by using the signals from the separate channels to carry out various calculations and extrapolations, thus avoiding the necessity to obtain image results at each location in the image space or in K-space. Some of these parallel imaging techniques are known as SMASH and SENSE and GRAPPA.
To obtain better images, the preamplifiers are located as close to the coil elements as possible. Although the size of MR preamplifier is greatly reduced recently, it still takes much space of overall array coil. In addition the area of coil enclosure at preamplifier must be rigid.
The coil cable, as is well known, consists of multi-coaxial cable and signal control wires and outer shield. Common mode current or shield current will be generated on outer surface of the shield during transmit phase by the high RF field generated by the transmit coil. To prevent the patient from being overheated dangerously by shield current, cable traps are required for the coil cable assembly. Longer cable with more cable traps is required for the clinic applications, such as intra-operative MR imaging on a moving magnetic system.